Behavior of Partly Crystallized Basaltic Magma Based on a Field and Laboratory Study of a Thick Flood Basalt

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9628269 Philpotts It is proposed to investigate four different profiles through the Holyoke basalt using chemical analyses to define the degree of compaction and the partial melting technique to enhance textures for petrographic analysis. During compaction, the abundances of minerals and residual liquid change, but these phases are difficult to identify precisely in a thin section of crystalline rock. Yet it is important to know not only the abundance of liquid at a given stage of compaction, but also its distribution. In preliminary experiments on the Holyoke basalt, the P.I. found that by partly melting a sample, a clear picture of the amount and distribution of residual liquid can be obtained as a function of temperature. The experiments show that the crystal mush consisted of a network of chains of refractory minerals surrounding channels of liquid. In the experiment, the intrinsic permeability of the mush could also be determined. When applied to rocks that have undergone different degrees of compaction, the technique has the potential of determining how the solids and liquid redistributed themselves during compaction and thus of revealing the mechanisms involved. The results will provide quantitative data on the mechanisms and rates of compaction of crystal mush formed from quartz tholeiitic magma. Although determined with data from a surface flood-basalt flow, the results will be applicable to processes acting in the earth.